Material and its influence on the friction coefficient

Transcription

1 APi Pin-on-disc Study of the Rusts on Wheel Rail Material and its influence on the friction coefficient ; Ulf Olofsson Department of Machine Design; KTH Railway Group Royal linstitute t of Technology (KTH) 1

2 Control of the friction coefficient Maintenance of the wheel-rail interface Vehicle operation Importance Influential factors: environment; third-body; material properties Measures: friction modifier; lubricant; grinding Rustand oidela oxide layers 2

3 What is rust? Rust is hydrated iron oxides. Iron oxides refer to anhydrous iron oxides. 3

4 ----D. Godfrey, Iron oxides and rust in tribology, Technical paper, Journal of the society of tribologists and lubrication engineers 1999; 55(2);

5 Rusts on rails: Different rusts and iron oxides on the rail can result in various friction coefficient causing stick-slip slip which leads to rail corrugations. ---M. Ishida, et. al, Rail corrugations caused by low coefficient i of fiti friction in a submarine railway tunnel. It was reported that β-fe 2 O 3 H 2 O which is generated under the moist environment with the presence of chloride (Cl) has a great impact on reducing friction coefficient. A detailed surface treatment was also suggested. ---J. Suzumura, et. al, In situ X-ray analytical study on the alteration process of iron oxide layers at the railhead surface while under railway traffic, Wear 271 (2011)

6 Two exposures:(pins and discs are made of wheel rail materials) Group1 G1 (five cycles) Group 2 for comparison G2 (five cycles) Step 1 exposure in air for 0.5 h at 40 C and RH> 90% exposure in air for 2 hours at 40 C and RH > 90% Step 2 exposure in air for 0.5 h with 1% NaCl solution spray at 40 C and RH> 90% exposure in air for 6 hours at 40 C and RH< 30% Step 3 exposure in air for 1 h at 40 CC and RH> 90% Step 4 exposure in air for 6 h at 40 C and RH< 30% 6

7 G1 exposure G2 exposure 7

8 XRD X-ray diffraction analysis? G1 6 disc 500 G1 6 pin (Cps) Lin ? Lin (Cps) Theta - Scale G1 6 disc (*) - Lepidocrocite, syn - Fe+3O(OH) - Orthorhombic - Base-centered - Bbmm (63) - I/Ic PDF S-Q (*) - Magnetite, syn - Fe2.93O4 - Cubic - Face-centered - Fd-3m (227) - I/Ic PDF S-Q 19.4 % (*) - Iron - Fe - Cubic - Body-centered - Im-3m (229) - I/Ic PDF S-Q 12.6 % (I) - Goethite, syn - FeO(OH) - Orthorhombic - Primitive - Pbnm (62) - I/Ic PDF 3. - S-Q 2.6 % Theta - Scale G1 6 pin (*) - Iron - Fe - Cubic - Body-centered - Im-3m (229) - I/Ic PDF S-Q 55.7 % (*) - Maghemite-C, syn - Fe21.333O32 - Cubic - Primitive - P4332 (212) - I/Ic PDF S-Q 17.4 % (*) - Lepidocrocite, syn - Fe+3O(OH) - Orthorhombic - Base-centered - Bbmm (63) - I/Ic PDF S-Q (I) - Goethite, syn - FeO(OH) - Orthorhombic - Primitive - Pbnm (62) - I/Ic PDF 3. - S-Q 4.3 % 1100 G2-1 disc 500 G2-1 pin Lin (Cps) Lin (Cps) ? Theta - Scale G2-1 disc (*) - Iron - Fe - Cubic - Body-centered - Im-3m (229) - I/Ic PDF S-Q 92.7 % (I) - lepidocrocite - FeO(OH) - Orthorhombic - Base-centered - Cmcm (63) - I/Ic PDF S-Q 7.3 % Theta - Scale G2-1 pin (*) - Iron - Fe - Cubic - Body-centered - Im-3m (229) - I/Ic PDF S-Q 94.4 % (*) - Manganese Carbide - Mn23C6 - Cubic - Face-centered - Fm-3m (225) - I/Ic PDF S-Q 5.6 % 8

9 Treatment Conditions Generated Generated from ref. Sprayed salt solution (1%) for half an hour 40 C, 2 hours with high humidity, 6 hours with low humidity. 5 cycles No salt solution α-fe 2 O 3 H 2 O α-fe 2 O 3 H 2 O γ- Fe 2 O 3 H 2 O β-fe 2 O 3 H 2 O Fe 3 O 4 γ- Fe 2 O 3 H 2 O γ- Fe 2 O 3 Fe 3 O 4 γ- Fe 2 O 3 H 2 O α-fe 2 O 3 H 2 O γ- Fe 2 O 3 H 2 O Fe 3 O 4 ---K. Ohno, Y. Ogawa, RTRI Rep., No. A-83-70,

10 Pin-on-disc testing: Contact pressure: 900MPa; Sliding speed: 0.01m/s Pin-on-disc testing with two temperature 20 C (+) and 10 C (-) with RH 40%±5%; with water (w) and dry (d) Test duration: 30min Sliding distance: 18m 10

11 Friction results: 11

12 In one of the tests, interesting results are observed! G2 exposure (thin oxide, 10 C): 12

13 More tests are done with regard to different levels of humidity: On the thin oxide specimens at 10 C Water lubricated Specimens Height Width [mm] [mm] 35% % mm 1mm 1mm 55% % 45% 55% 13

14 [Ref] O. Hayashi et. al, Influence of atmospheric conditions upon adhesion between rails and running wheels, Nippon Kikai Gakkai Ronbunshu, C Hen/ Transactions of Japan Society of Mechanical Engineers, Part C 63 (606), pp

15 Discussioni 1 for thick oxide specimens, µ is almost independent of lubricants (dry or water), especially at room temperature. The running-in process is also independent of the environmental conditions. These phenomenons are probably due to the extremely rough surface topography. 2 for thin oxide specimens, the running-in process lasts only for a very short while (< 2min, sliding distance around 1 meter) under dry condition. However, under wet condition, the running-in i process lasts long. 3 thin oxide specimens are very sensitive to relative humidity. 15

16 Future work: 1 more tests will be done for thin oxide specimens at various humidity levels; temperature levels. 2 surface analysis 16

17 Thank you for your attention! 17